This invention pertains to the field of pressure regulation.
The art of regulating gases or liquids from a higher pressure to a lower pressure has not seen many advances in the modem day. Generally, a pressure regulator is built using a cylinder together with a piston. The piston is used to actuate a valve, normally consisting of a spherical ball that rests in a circular seat. The present invention is useful for regulating the delivery pressure of liquids and gases. In the interest of brevity, much of the discussions presented herein refer only to gas pressure.
Visualizing the piston in an upright position with the piston rod oriented downward and acting on the spherical ball, regulated gas pressure acts against the underside of the piston. As the gas pressure under the piston falls, a spring forces the piston downward. This, in turn, opens the gas valve allowing the pressure to rise. The pressure setting for the regulator is adjusted by manipulating the amount of spring force acting upon the piston. In order to facilitate adjustment of the spring force acting downwardly on the piston, a spring stop is moved linearly along the non-pressure side of the cylinder that houses the piston. The gas pressure is contained below the piston by a rudimentary sliding seal between the outer perimeter of the piston and the inner wall of the cylinder.
In the known art, the seal material used most commonly is a rigid material. The rigid material, in many cases a carbon ring, is set into a groove machined into the piston and, having a minimum amount of pliancy, establishes a seal through a combination of normal and axial forces between the inner wall of the cylinder and the surfaces of the groove machined into the piston. A bellows has been used as an alternative to rigid piston rings. In these prior art regulators, a bellows is attached to the piston and to the inner wall of the cylinder. Each of these two known methods of containing the pressure under the cylinder are cursed with several undesirable attributes.
In the case of a rigid carbon ring, the pressure containment achieved is quite satisfactory. However, the use of such a rigid seal introduces heavy forces that must be overcome in the regulation process. In efforts to minimize these forces, the inner wall of the cylinder must be polished and coated with specialized lubricants. This reduces the break-away friction that must be overcome whenever the pressure must be adjusted. Use of a bellows essentially eliminates the hysteresis that results from this break-away friction phenomenon. A bellows seal, though, allows the bore area of the resultant regulator to vary. This causes an undesirable, non-linear regulation response.
The problems of hysteresis and non-linear response may not affect the majority of regulator applications, but they are significant obstacles in the art of precision regulation. This is especially true when the precision regulator is called upon to deliver a reference pressure of high caliber. Regulation hysteresis can render the precision reference ineffective due to the wild pressure swings that are exhibited every time the break-away friction in the cylinder seal is breached. The bellows seal is also inappropriate for precision reference applications because of the possibility of pressure oscillations attributable to the non-linear response of these regulators.
What is needed is a means of sealing the pressure side of a piston operating in a cylinder so that the frictional forces acting in the linear axis of the piston are minimized. This must be accomplished concurrently with the maintenance of a constant bore area for the regulator to balance the spring force. By achieving these two objectives, hysteresis effects can be mitigated and pressure oscillations resulting from a non-linear regulator response can be avoided.
The present invention comprises an apparatus for regulating pressure and a method of manufacturing said apparatus.
One aspect of the present invention is a piston seal that is composed of a pliable material. Any number of pliable materials are acceptable, but the present invention is best embodied using any one of a wide variety of pliable materials such as rubber, urethane, composite materials and even animal tissue or plant fiber. It should be noted that this list of possible pliable materials is meant to be illustrative and should not be construed as limiting the scope of the present invention. The pliable material is formed into a continuous seal with a cross section having several novel features. The cross section comprises a pair of apexes, one associated with an inner wall while the other is associated with an outer wall.
The cross section profile further comprises a concave depression disposed between the two apexes. A pressure cell is formed by the perimeter defined by the inner and outer walls immediately under the two apexes and the concave depression. The inner and outer walls drop tangentially from the radius of each apex to the base of the profile. The inner and outer walls further comprise a feature that they rise from the base sloped toward the center of the radii of their respective apexes.
The present invention further comprises a pressure regulator that incorporates the new pliable seal. This pressure regulator comprises a cylinder and a piston. Each of these elements has a seal receptacle that receives the pliable seal comprising, among other features, the two apexes. Ordinarily, the groove in the cylinder wall is disposed in a manner to correspond to the seal seat of the piston as the piston hovers about at an equilibrium position.
As the pliable seal is installed into the seal seat of a piston, one or both of the two apexes make a rolling contact with the upper surfaces of two receptacles, referred to as an annular internal groove on the cylinder internal wall or a seal seat on the piston. The depression disposed between the two apexes reduces the possibility that the pliable material will be sheared through when the piston moves axially within the cylinder. The regulator further comprises inlet and outlet ports for accepting high-pressure gas or liquid and discharging gas or liquid at a lower regulated pressure.
The pressure regulator according to the present invention uses the regulated pressure of discharged gas or liquid to further activate the piston seal. The pressurized gas or liquid acts on the piston seal to further increase the contact force between the piston seal and the piston. This same mechanism is used to increase the contact force between the piston seal and the cylinder. To aid this process, a convex surface defines the boundary of the pressure cell and this convex surface helps to ensure that pressure forces are transferred to the contact points rather than merely deform the profile of the piston seal.
Because the cross-sectional area of the new seal can be compressed into the cross sectional area of the seal seat disposed on the outer perimeter of the piston, the present invention includes a new method for manufacture of regulators incorporating the new pliable piston seal. This method defines the steps of fabricating a regulator with receptacles to accept the pliable seal in both the piston and the cylinder so that the two grooves correspond when the piston is in an equilibrium state. This process is augmented by installation of the pliable piston seal by compressing same into the cavity of the seal seat in the piston and then inserting the piston into the cylinder while the seal is so compressed.